Ultrahigh-frequency cavity resonator



May 1953 s. s. HELLER 2,639,327

ULTRAHIGH-FREQUENCY CAVITY' RESONATOR Filed June 7, 1945 INVENTOR. GERALD S. HELLER MAX/m g LAX/K ATTORWEV Patented May 19, i953 UNITED PATENT i OFFICE ULTRAHIGH-FR-EQI'JENCY caviar. V v RESONATOR Gerald S1 Heller, Cambridge, Mass'., assi-g'nor, by mesne assignments, to the United State of America asrp're'seiited by theSecretary of War Application June a, 1945, seriai schist This invention relates to electrical pparatus and more particularly to ultra high frequency cavity resonators.

In accordance with conventional practice certain devices known as cavities may be used as resonant circuits. Such a cavity is generally circular in cross-section and may be thought of as a section of circular wave guide shorted at both ends. It is often desired to operate the cavity in modes higher than its dominant mode of operation. As is well understood in the art, however, when modes of operation other than the dominant mode are desired, the cavity will have a tendency to operate also in the lower modes.

It is an object of this invention, therefore, to provide, in a cavity resonator, a mode damper for minimizing the aforestated undesired effects.

In accordance with the present invention there is provided a plurality of absorptive and dissipative rings placed within the base of a cavity at points of minimum field intensity of the desired mode.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing in which:

Fig. 1 shows schematically the configuration of the electric field at a given instant within a cavity operated in the TEo,s mode;

Fig. 2 shows the variation of electric field intensity along the line 22 of Fig. 1;

Fig. 3 shows the configuration of the electric field at a given instant for an undesired mode, such as TEo,1, within the aforesaid cavity;

Fig. 4 shows the variation of electric field intensity along the line 4-4 of Fig. 2;

Fig. 5 is a sectional View of the base of the aforesaid cavity equipped with absorptive and dissipative rings, the electric field variations of the TE0,1 and TE-0,3 mode being indicated thereon; and

Fig. 6 is a plan view of the cavity base of Fig. 5.

Referring now more particularly to Figs. 1 and 2 of the drawing, there are shown the configuration and variation of the electric field within a cavity designed to be operated in the TE0.3 mode. The variation of field intensity, of which line [2, l3 and I4 indicate the maxima, is represented by the curve I5, Fig. 2. The distribution theoretically follows a Bessel function, but for simplicity of illustration it is here represented as sinusoidal whereby the points l6, l1, l8, l9 and of zero field intensity are evenly spaced, this being approximately correct for present purposes.

sonata. (01.178-44.)

Referringnow to Figs; 3 and 4, there is shownthe field" configuration a-iid intensity variation of an undesired lower mode in the cavity H, the mode shown being the TEo,1. The lines 25 indicate the maxima of the electric field and the sinusoid 26 indicates the varition along the line 4-4 of Fig. 3.

In Figs. 5 and 6 the cavity II with its base 3| is shown with absorptive rings 32 and 33. The rings are inserted in the base 3| of the cavity II and may be made of Polyiron or similar absorptive and dissipative material. Referring to the superimposed sinusoids I5 and 26, Fig. 5, it will be noted that the rings 32 and 33 are placed at minimum point-s I6, l1, l9 and 20 of the desired field distribution. When this is done, the undesired mode represented by curve 26 is highly absorbed and dissipated by the rings 32 and 33 and hence greatly reduced in its magnitude, Whereas the desired mode (curve I5) is substantially unaffected.

It can be shown that the TEo,2 mode will also be minimized by this placement of the absorptive and. dissipative rings. The rings may be placed in either one or both ends of the resonator, and the invention is not confined to the particular modes assumed here for illustration of the invention.

While there has been disclosed what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention.

What is claimed is:

1. An ultra-high frequency device comprising a cavity resonator having conducting walls and being adapted to be resonant to ultra-high frequency electromagnetic wave energy in a plurality of modes and electromagnetic wave energy absorptive and dissipative means forming a part of the inner surface of said conducting walls at points at which the current flowing along the surface of said conducting walls for a desired one of said resonant modes is to be a minimum.

2. An ultra-high frequency device comprising a cylindrical cavity resonator having conducting walls and at least one conducting fiat base plate and being adapted to be resonant to ultra-high frequency electromagnetic wave energy in a plurality of 'I'Eo,n modes where n is a positive integer and at least one ring-shaped electromagnetic wave energy absorptive and dissipative means forming a part of the inner surface of said base plate, said ring-shaped means being mounted concentrically with said cylindrical resonator and having a radius substantially equal to the distance from the center of said resonator to a point at which the current along the surface of said base plate is to be a minimum for a desired one of said resonant modes.

3. An ultra-high frequency device comprising a cylindrical cavity resonator adapted to be resonant to ultra-high frequency electromagnetic wave energy in a plurality of 'I'Eo,n modes where n is a positive integer, said resonator having at least one flat end plate, and first and second ring-shaped electromagnetic energy absorptive and dissipative means forming part of the. inner surface of said base plate concentric With one another and with said cylindrical resonator and having respectively radii of substantially one-- third and two-thirds of the radius of said cylindrical resonator.

4. In combination, a wave guide, a conductive end; plate therefor and an extraneous mode suppressor comprising a slot in said plate located in 4 a nodal region for IE0 mode oscillations and dissipative material connected to said end plate, and in contact therewith.

5. Incombination, a wave guide adapted to be resonant to electromagnetic wave energy in a plurality of modes, a conductive end plate therefor, and electromagnetic'wave energy dissipative means in contactrwith the surface of said end plate in a nodal region for a desired one of said modes.

GERALD S. HELLER.

References Cited in the file of this patent UNITED STATES PATENTS Date 

